Semiconducting europium-and/or ytterbium-containing sulfides and selenides of pseudo-orthorhombic crystal structure

ABSTRACT

DISCLOSED HEREIN ARE EUROPIUM- AND/OR YTTERBIUMCONTAINING TETRACHALCOGENIDES OF PSEUDO-ORTHORHOMOBIC CRYSTAL STRUCTURE, AND A PROCES THEREFOR. SAID TETRACHALCOGENIDES, USEFUL AS SEMICONDUCTORS AND AS LUMINOPHORS, HAVE THE FORMULA   MQ2X4   WHEREIN: M IS SELECTED FROM AT LEAST ONE OF EU AND YB, Q IS SELECTED FROM AT LEAST ONE OF AL, GA AND IN, X IS SELECTED FROM AT LEAST ONF OF S AND SE, AND WITH THE PROVISO THAT WHEN M CONSISTS OF OR INCLUDES YB, THEN Q IS SELECTED FROM AT LEAST ONE OF AL AND GA.

United States Patent 3 801 702 SEMICONDUCTING ElJRdPIUM- AND/ OR YTIER- BIUM-CONTAINING SULFIDES AND SELENIDES 0F PSEUDO-ORTHORHOMBIC CRYSTAL STRUC- TURE Paul C. Donohue, Montclair, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Filed Apr. 30, 1971, Ser. No. 139,181 Int. Cl. C09k 1/12, N16 US. Cl. 423-263 13 Claims ABSTRACT OF THE DISCLOSURE Disclosed herein are europiumand/or ytterbiumcontaining tetrachalcogenides of pseudo-orthorhombic crystal structure, and a process therefor. Said tetrachalcogenides, useful as semiconductors and as luminophors, have the formula wherein M is selected from at least one of Eu and Yb,

Q is selected from at least one of Al, Ga and In,

X is selected from at least one of S and Se, and with the proviso that when M consists of or includes Yb, then Q is selected from at least one of Al and Ga.

BACKGROUND OF INVENTION 1. Field of the invention This invention relates to novel sufides and selenides that contain europium and/or ytterbium, to a novel process therefor, and to the use of said sulfides and selenides as semiconductors and as luminophors.

2. Description of the prior art Particular combinations of properties required in semiconductors in specific applications are so demanding that new compositions are continually being sought. This invention is concerned with new, isotypic semiconducting compositions which, in addition, luminesce in the visible region of the spectrum upon irradiation with UV light or sunlight.

Certain tetrasulfide and tetraselenide compositions are known, including some that contain one or more of the metals taught herein. References to some of these compositions are given below. None of these references teaches or suggests any of the particular compositions disclosed herein or the process for making them.

All of the following references concern tetrachalcogen compositions:

(a) R. Eholie, et al., C. R. Acad. Sci., aris, Ser. C, 268,

(b) H. Hahn, et al., Z. Anorg. Allg. Chem. 263, 177

(c) J. Flahaut, Comptes Rendus 233, 1279 (1951) and J. Flahaut, Ann. Chim., Ser. 12, T., 7 682 (1952), (d) H. Hahn, et al., Z. Anorg. Allg. Chem. 279, 241

(e) L. Krausbauer, et al., Physica 31, 113 (1965), (f) C. K. Jorgensen, et al., J. Chem. Phys. 62, 444

(1965), and (g) C. Romers, et al., Acta Cryst. 23, 634 (1967).

The combination of luminescence and semiconductivity characteristic of the products of this invention is attributed to the presence of divalent Eu and/or Yb and to the unusual crystal structure resulting from chemical combination of the relatively large and highly ionic divalent Ca, Sr, Ba, Eu and Yb cations and the smaller, more covalent, trivalent Al, Ga, and In cations with sulfur and selenium anions. It is surprising and especially note- 31,801,702 Patented Apr. 2, 1974 worthy that the novel Eu-containing compositions fluoresce in daylight, being activated by visible light, a property usually exhibited only by certain organic compositions.

SUMMARY OF THE INVENTION 1. Product The novel tetrachalcogenide compositions of this invention are characterized by their isotypic pseudo-orthorhombic crystal structure and formula:

r-y Q2 4 wherein M is selected from at least one of En and Yb,

Z is selected from at least one of Ca, Sr, and Ba,

Q is selected from at least one of Al, Ga, and In, X is selected from at least one of S and Se, and y is 0.0001 to 1,

with the provisos that:

(1) when Z consists of or includes Ca, then Q is Ga;

(2) when M consists of or includes Yb, then Q is selected from at least one of Al and Ga; and

(3) when Z consists of or includes Ba and X consists of or includes S, then at least 50 atomic percent of Q is In.

The minimum quantity of europium and/or ytterbium (wherein y is at least 0.0001) has been found to insure the bright luminescence of the novel compounds.

An alternative description of the novel compositions of this invention is according to the formula wherein:

M consists of at least 0.01 atomic percent -Eu and/or Yb and up to 99.99 atomic percent Ca, Sr and/or Ba, Q is selected from at least one of Al, Ga, and In, and X is selected from. at least one of S and Se, with the provisos that:

(1) when M includes Ca, then Q is Ga; (2) when M consists of or includes Yb, then Q is selected from at least one of Al and Ga; and 3) when M includes Ba and at the same time X consists of or includes S, then at least 50 atomic percent of Q is In.

2. Process Compositions of the present invention are prepared by heating together at about 750 to 1300 C., appropriate, approximately stoichiometrically required quantities of reactants selected from (a) elementary Eu, Yb, Ca, Sr, Ba, Al, Ga, In, S and Se,

(0) chalcogenides of the formula Z(S,Se) where Z is Ca, Sr, Ba, or Eu; and Q (S,Se) where Q is Al, Ga or In,

(0) polynary tetrachalcogenides represented by the formula (Eu,Yb,Ca,Ba,Sr) (Al,Ga,-In) (S,Se) (especially useful when preparing chalcogenides containing more than 4 elements), and

(d) combinations of the above.

In the formulas written above and hereafter in this application, atoms which may replace each other are separated by a comma and placed between parentheses as described in Definitive Rules for Nomenclature of Inorganic Chemistry, I. Am. Chem. Soc. 82, 5532 (1960). Thus the symbol (ALGa) denotes the complete range from pure Al to pure Ga.

Reaction is customarily eifected under nonoxidizing conditions in the absence of air, conveniently in silica tubes which have been charged, evacuated, and sealed. Since certain of the elementary reactants have some tend ency to react with silica at the elevated temperatures required for reaction, it is advantageous, though not essential, to precoat the inside of silica tubes with carbon, for instance, by pyrolyzing a hydrocarbon therein; or, the reactants may be placed in an inert vessel such as a graphite, alumina, or zirconia crucible which is placed in an evacuated reaction vessel. When very high temperatures are desired, the reactants may be placed within induction-heated graphite crucibles located in evacuated and sealed vessels which may be silica vessels if they are insulated from the crucibles or otherwise provided with cooling means.

The time of heating is not critical but should be sufficient for complete reaction. At temperatures of 1000 to 1200 C., 24-96 hours usually sufiices for complete reaction though the heating time may be extended if desired. When elementary selenium and, especially sulfur, which have relatively high vapor pressures are employed as reactants, it is desirable to maintain a temperature gradient in the reaction tube to permit unreacted chalcogen to condense in the cooler end of the tube.

After the chalcogen has reacted, the reactor may be heated uniformly. The hotter end of the tube may, for example, be held initially at about 750 to 1000 C. with the cooler end at 300 to 800 C. The preliminary reaction of the chalcogen may take up to 12-24 hours or more after which the temperature may be raised to about l1200 C. to complete reaction. The temperature gradient may be achieved by partially inserting the reaction tube into the furnace, by employing a furnace with a natural temperature gradient, or .by employing a furnace with zones held at different temperatures. Once elementary chalcogen has reacted, the tube may, if desired, be cooled and opened and the product ground and fired again. This sometimes affords a more homogeneous product. A temperature gradient is not required when free chalcogen is not employed, as for example in the reactions represented by Equations (5), (6), (8), (l) and (11) below.

Pressure is not critical and the reaction can be effected at autogenous pressure in reactors that have been evacuated and shut or sealed prior to reaction.

Use of highly pure reactants is not essential and, dependent upon the desired purity of product, reactants ranging from commercial grade to ultrahigh purity grades may be employed. The reactants are preferably powdered and well mixed before heating is commenced.

Some typical reactions that yield the products of the invention are:

( +A12S3 +In S 2Ba Eu' Al'InS (ll) 0.85BaS+0.15EuS+0.25Ga S +O.75In S Ba Eu Ga In S (12) 0.9EuS+0.05SrS+0.05BaS+0.5Al Se -|-0.5In Se S1' Ba Eu AlIn,SSe DETAILS OF THE INVENTION 1. Product The novel products of this invention include the ternary compositions EuAl S EuAl Se EuGa S EuGa Se Euln S EUIHZSE4, YbA12S4, YbAl Se YbGa S and YbGa Se and their solid Solutions with each other. In

addition, polynary products of the invention include solid solutions derived from as little as 0.00011 mole of any of the above ternary chalcogenides or their solid solutions with each other, with up to 0.9999 mole of one or more of where x is equal to at least 1. It is to be understood that solid solutions of this invention are homogeneous compositions of single crystalline phase and not simply mixtures. Complete solid solution of one phase in another is meant, e.g., of y moles of EuGa Se in (l -y) moles of SrIn S to give pseudo-orthorhombic-type crystals of Sr Eu Ga In Se S or if y=0.3, single phase crystals of (SI0,q o.3) (Ga In )(Se S Similarly, y moles of YbGa S; disolves in l-y moles of CaGa S to give Ca Yb Ga S Generic formula .All products of the invention are described by the general formula 1-y yQ2 4 wherein:

M is selected from at least one of En and Yb, Z is selected from at least one of Ca, Sr, and Ba, Q is selected from at least one of Al, Ga, and In, X is selected from at least one of S and Se, and y is 0.0001 to 1,

with the provisos that:

(1) when Z consists of or includes Ca, then Q is Ga,

(2) when M consists of or includes Yb, then Q is selected from at least one of Al and Ga, and

(3) when Z consists of or includes Ba and at the same time X consists of or includes S, then at least 50 atomic percent of Q is In.

Subgeneric formulas When y=1, and accordingly "Ca, Sr, and Ba are absent, products of the invention can be represented by the subgeneric formulas: I

When y is 0.0001 to less than 1, products of the invention may be represented by the following subgeneric formulas:

In the above Formulas A4 and throughout this specification, it is to be understood that elements placed between parentheses and separated by commas may replace each other in any proportion provided the overall stoichiometry required by the formula is preserved.

All compositions falling within the scope of the invention will not be listed specifically. By way of illustration, however, compositions falling under Formulas A, B, C and D above will be specifically listed, and a selected group of compositions and subgeneric formulas describmg them will be given in Table I. It should be remembered that the relationships between Z, M, Q and X are determined according to the formula Z M Q X wherein y=0.000l t0 1.

Compositions represented by Formula A are as follows:

Eu (Al, Ga, In) (S, Se) Eu (A1, Ga, In) S Eu (Al, Ga In) Se Eu (A1, Ga) (s, Se) Eu (Al, Ga) S Eu (Al, Ga) Se Eu (Al, In) (S, Se) Eu In) S Eu (Al, In) Se Eu a, In) (5, Se) Eu (Ga, In) 8 Eu (Ga, In) Se Eu A1 (S, Se) Eu A1 S Eu Al Se Eu Ga (S, Se) Eu Ga S Eu Ga Se Eu In (S, Se) Eu In S Eu In Se M Q X Yb (Al, Ga) (S, Se) Yb (Al, Ga.) S Yb (Al, Ga) Se Yb A1 (S, Se) Yb Al S Yb Al Se Yb Ga (S, Se) Yb Ga S Yb Ga Se Compositions falling under Formula C that are not included in the compositions falling under (A) and (B) are as follows:

M Q X (Eu, Yb) (Al, Ga) (S, Se) (Eu, Yb) (A1, Ga) S (Eu, Yb) (Al, Ga) Se (Eu, Yb) Al (S, Se) (Eu, Yb) Al S (Eu, Yb) Al Se (Eu, Yb) Ga (S, Se) (Eu, Yb) Ga S (Eu, Yb) Ga Se Compositions falling under Formula D are as follows:

(Ca, Sr, Ba) (Eu, Yb) Ga. Se (Ca, Sr, Ba) Eu Ga Se (Ca, Sr, Ba) Yb Ga Se (Ca, Sr (Eu, Yb) Ga Se (Ca, Sr) Eu Ga Se (Ca, Sr) Yb Ga Se (Ca, B (Eu, Yb) Ga Se (Ca, Ba) Eu Ga Se (Ca, Ba) Yb Ga Se (Sr, Ba) (Eu, Yb) Ga Se (Sr, Ba) Eu Ga Se (Sr, Ba) Yb Ga Se Ca (Eu, Yb) Ga Se Ca Eu Ga Se Ca Yb Ga Se Sr (Eu, Yb) Ga Se Sr E11 Ga Se Sr Yb Ga Se Ba (Eu, Yb) Ga Se Ba Eu Ga Se Ba Yb Ga Se In Table I are listed selected compositions and the subgeneric formulas that described them:

TABLE I Subgenerle Formula Z M Q Ga Ga (A1,, Ga In (Al, Ga In) l, Gab, n) Ga (Al, Ga)

(Al, Ga)

( l, b, c) (A 1 h, Gas, Ga

(A) Product identity Product identity is conveniently established by Debye- Scherrer X-ray powder diffraction technique and/ or Buerger precession camera technique, the X-ray patterns being compared with that of a previously-identified tetrachalcogenide. Patterns were generally read and cell constants refined using a computerized least-squares technique. Cell constants and cell volumes are reported in Table HI.

Single crystal X-ray methods indicate that an orthorhombic cell can be used to index most of the peaks of the X-ray powder diffraction patterns of the novel products taught herein. All peaks can be indexed by using an orthorhombic cell in which all the axes are doubled. Careful investigation of single crystal data indicates that systematic absences of reflections do not conform to any orthorhombic space group and suggests that the observed orthorhombic symmetry is due to crystal twinning. The actual symmetry is lower than orthorhombic and either monoclinic or triclinic. Thus the orthorhombic cell is a pseudo cell which is useful for phase identification and for determining relative cell volumes.

The compositions of this invention have crystal structures indexable on the basis of pseudo-orthorhombic crystal cells with cell constants of a: 10.0- 11.3 A. b=6.06.8 A. c=10.01l.34 A.

cell volume=600870 A.-*.

(B) Homogeneous products containing small quantities of rhombohedral tetrachalcogenides Tetrachalcogenides of related but distinctly different chemical composition and crystal structure are described in coassigned application, CR 7090-B, filed herewith. Therein is described and claimed semiconducting compositions of rhombohedral-type crystal structure and formula wherein A consists of 80 to 100 atomic percent Ba, and to 20 atomic percent of one or both of Sr and Eu, and

0 to atomic percent of one or both of Ca and Yb,

Q consists of 66 to 100 atomic percent of one or both of Al and Ga and 0 to 34 atomic percent In; and

X consists of 10 to 100 atomic percent S and O to 90 atomic percent Se.

Up to about 1 mole percent by weight of these compositions of CR 7090-B may be homogeneously incorporated into the pseudo-orthorhombic-type compositions of the present invention. Incorporation of increasingly larger quantities results first in a mixture of semiconductive pseudo-orthorhombic and rhombohedral-type crystal phases and finally when the concentration of Z M Q X becomes low, in homogeneous products of rhombohedraltype crystal structure.

(C) Polyphase products Semiconductors with polyphase structures and empirical chemical compositions intermediate between those of the present invention and those of coassigned application CR 7090-B may be prepared by methods described for the instant invention without change other than employing the ingredients in quantities theoretically capable of giving the desired product. Typical of such intermediate products are polyphase compositions of empirical formula 0.25 0.75 2 4! as as z o and o.7 o.3 4-

Intermediate compositions usually exhibit the X-ray diffraction patterns of both pseudo-orthorhombic and rhombohedral-type phases and, in fact, are usually separable manually into discrete phases, one giving a pseudoorthorhombic-type X-ray diffraction pattern and the other a rhombohedral-type X-ray dilfraction pattern. For example, reaction of a mixture of BaS, EuS, Ga and S in 0.5:0.5:2:3 formula weight ratio and 0.05 g. iodine for 96 hours in an evacuated, sealed silica tube with one end of the tube at 860 C. and the other end at 500 C. resulted in a yellow-green product that fluoresced in daylight. The product was manually separated into two fractions, one of which emitted green light and the other yellow light upon exposure to UV radiation. The yellowemitting material gave an X-ray diifraction pattern typical of pseudo-orthorhombic EuGa S but with some shifting of lines indicative of a slightly larger crystal cell. The fraction that fluoresced in the green gave an X-ray powder diffraction pattern like that of rhombohedral-type BaGa S but with shifting lines indicative of formation of a smaller cell.

(D) Doping Compositions of the invention may be doped to alter semiconductivity (e.g., to lower their resistivity) and/or fluorescence (e.g., to change the color or shade of emitted radiation). This may be accomplished by bringing about a slight imbalance in the ideal stoichiometric ratio of 1M:2Q:4X or by introducing a foreign ion into the crystal lattice. The imbalance may be achieved by slightly altering the theoretically required quantities of reactants, and small quantities of foreign ions may be introduced simply by having them present during synthesis. In either case, synthesis is effected in the usual manner. Alternatively, a product of the invention may be calcined in contact with or in the vapor of one of its elemental components or a foreign element. Another route is to dope a starting material of the type described in Table II and then use the doped material as a reagent in preparing products of the invention.

Dopants may be chosen to partially occupy one or more lattice positions in Z M Q X where Z, M, Q, X and y have their previously designated meanings. Thus, Z, and possibly M, may be partially replaced by large cations with ionic radii of about 0.9-1.5A, e.g., by rare earth metals of atomic number 57-71 (exclusive of Eu and Yb), Na, K, Rb, Bi, Pb, U, Cd, Hg, Ag, and Au. Smaller cations with ionic radii of 0.4 to less than 0.9A. may be partially substituted for Q metals; these include the transition elements of atomic numbers 21-30, 39-46, and 72- 78, and Si, Ge, and Sn from Group lV-A of the Periodic Table. Typical anionic elements that may partially replace sulfur and selenium include Cl, Br, I, Te, P, As and O.

The quantity of dopant required to alter fluorescence and/ or semiconductive properties is generally small, ranging from less than 0.002 to about 1 atomic percent of the element that is partially replaced. If desired, more than one dopant may be incorporated simultaneously. Incorporation of dopants is exemplified in Examples A, D and E.

2. Process Binary sulfides and selenides of Formula ZS and ZSe where Z is Eu, Ca Sr and Ba suitable for use as reactants, are well known.

The sulfides and selenides A1 8 Al Se Ga S Ga- Se In S and In Se are also well known. Their preparation is described, for example, by G. Brauer in Handbuch der .Pr'ziparativen Anorganischen Chemie, Ferdinand Enke Verlag Stuttgart, 1954.

Preparation of ternary and polynary tetrasulfides and tetraselenides which may themselves be used in preparing the products of the invention, e.g., by reactions such as When free sulfur or selenium is used as a reactant, it is desirable to heat initially somewhat below maximum temperature to avoid excessive pressure buildup and to permit uncombined sulfur and selenium to condense in the cooler end of the reactor. Free sulfur-containing systems usually require somewhat lower initial temperatures than selenium-containing systems. Rather than maintaining a temperature gradient, temperatures may be raised gradual- 1y over a period of hours from about 600 C. to a maximum temperature of above 1200" C. Alternatively, a period at moderate temperature (about 600 C.) may be followed by a period at maximum temperature.

When elements are employed as reactants, it is desirable, though not imperative, to add a small quantity of iodine to the reaction mixture, e.g., about 0.05 g. per gram of total charge. The iodine may promote reaction by preventing formation of sulfide crusts rather than acting simply as a transport agent. It may in ad-v dition form small fiuxing quantities of Z1 Alternatively, small quantities of the halides of divalent Eu, Ca, Sr, or Ba or trivalent Al, Ga, or In may be employed as fluxes to permit the use of lower reaction temperatures and the formation of larger crystals of product.

The products of the invention usually form in the hot zone of the reaction vessel as sintered or fused masses, which in some cases include single crystals. The products are removed after cooling and washed with water or solvents, e.g., aqueous potassium hydroxide, to remove impurities such as traces of selenium. Crystal growth is sometimes enhanced by cooling slowly, e.g., from a melt of the product.

Large crystals of many of the compositions of the invention may be grown from the melt. The melting points of EuGa S EuGa Se and of EuIn Se are, respectively, about 1215 C., 1110 C., and 1010 C., consequently crystals may be grown by placing the pre-prepared ma- 5 terial in a suitable container such as an alumina or graphite crucible, heating in vacuo above the melting point, and

which may be cooled to initiate crystallization of material therein before the bulk of the material simply by slowly lowering the pointed end of the container out of the hot zone of the furnace.

3. Preparation of starting materials Preparation of some representative polynary starting materials is described in Table II. These materials have pseudo-orthorhombic crystal structures like those of the products of the invention.

TABLE II.PREPARATION OF SOME REPRESENTATIVE STARTING MATERIALS Prep. N 0. Composition Cell constants (A.) and cell volume (A!) Reactants Reaction conditions a b c i V Remarks A..... Sr Ga sei Br/Ga/Se in 1/2/4 atomic Brought slowly to 1,200 0. 10.711 6.385 10.864 742.9 Washed with dilute KOH.

ratio 0.05 g. I over 4 days in sealed, Product was brownishevacuated silica tube in wh t nongradient furnace. B..... SrImS. 0.5189 g. (0.00591 atom) Sr, Heated in sealed evacuated 10.548 6.510 10.439 716.9 Pink microcrystalline 1.3601g. (0.01185 atom) In, sihca tube in natural graproduct with t m 0.7597 g. (0.0237 atom) S, dient furnace for 3 days like that of Eu GazSi. 0.05 g. 1:. with 890 C. in hot Z0116 Small amt of red-black and 400 C. in cool zone. InzSi was also present. Reground and fired for 3 days with 950 C. in hot zone and 600 C. in cool zone. 'C-.'.-.-.. BaImS 0.1909 g. (0.001127 mole) BaS, Heated in sealed evacuated 10.840 6.556 10.885 773.5 Pink crystals formed in hot 0.2588 g. (0.002153 atom) In, sihca tube in natural grazone and small quantity 0.1084 (0.00338 atom) S, dient furnace for 2 days of red crystals in cool 0.05 g. g. with 1,000 C. in hot zone zone. The pink crystals and 600 C. in cool zone. had a structure like EuGazSi, and cell constants identifying them as Balnzs Red crystals rlirppseared to be largely 2 i. D srliri se 0.124 g. (0.00141 atom) Sr, Heated in graphite crucible 10.938 6.728 11.017 810.8 Washing product with 0.3251 g. (00283 atom) In, Within sealed, evacuated dilute KOH left dark 0.4471 g. (0.00566 atom) Se, silica tube in natural gm red-orange material which 0.05 g. I2. dient furnace for 2 days had the EuGBgS| with 1,000 C. in hot zone structure. and 800 C. in cool zone. E SrGaiS Br/Ga/S in 1/2/4 atomic ratio; Heated in A120: crucible in 10.255 6.107 10.424 652.8 Homogeneous red-pink 0.05 g. I silica tube for 3 days at product shown to be 930 C. and for 3 days at SrGazSi by analogy of 1,05 structure to that of EuGazsi. Some SrGazS preparations have fluoresced feebly in UN. light, seemingly because of trace amounts of unknown activators. F-.." Ca GazSe 0.0809 g. (0.00202 atom) Ca Heated in evacuated sealed 10.506 6.343 10.521 701.0 Product formed from the 0.2815 g. (0.00404 atom) Ga, silica tube 2 days with v melt in the hot zone 0.6376 g. (0.00808 atom) Se, 600 C. in hot zone and consisted of pink crystals 0 05 g. 1;. 400 C. in cool zone. Rewhich became clear white heated 2 days in the netupon washing with cone. ural gradient furnace with KOH. Structure and 000 C. in hot zone and density confirm the 800 C. in cool zone. formula. Density: calc., 4.69 g./cm. found, 4.66 g./cm. Semiconductor with Pisax 10 ohm-cm. G BaImSe 0.1662 g. (0.00121 atom) Ba, Heated in evacuated sealed 11.262 6.785 11.335 866.2 Product consisted of clear 0.2779 g. (0.00242 atom) In, silica tube in natural grato orange crystals inter- 0.3822 g. (0.00484 atom) Se, dient furnace for 2 days spersed with a little black 0.05 g. 1:. with 800 C. in hot zone material. The orange and and 600 C. in cool zone. clear crystals were identi- Reheated for 1 day with fled by X-ray diffraction. 1,000" O. in hot zone and 800 C. in cool zone. H..-" CaGazS 0.2605 g. (0.0065 atom) Ca, Heated 3 days in graphite cru- 10.026 5.97 10.215 611.0 Pink-white (3868254 formed (0.0130 atom) Ga, 0.9061 g. cible within evacuated in the hot zone.

' 0.8334 g. (0.026 atom) S, sealed silica tube in natural 0.05 g. 1 gradient furnace with 1,000 C. in hot zone and 900 C. in cool zone. I BaGmSe; 0.2118 g. (0.00154 atom) Ba, Heated in evacuated sealed 10.64 6.390 11.525 769.8 Sintered brownish product 1 0.2150 g. (0.00308 atom) Ga, silica tube for 2 days in nain hot zone had powder 0.487 g. (0.00616 atom) Se, tural gradient furnace with pattern like that o! 0.05 g.I 1,000 C. in hot zone and EuGazsi.

700 C. in cool zone. Beheated for 2 days with 1,000 C. in hot zone and 900 C.

- v in cool zone. J.'. SrAliSi 0.3042 g.(0.00347 atom) Sr, Heated in evacuated sealed 10.227 6.065 10.429 646.8 Orange flaky crystalline 0.1873 g. (0.00694 atom) A], silica tube for 2 days in naproduct with .X-ray difirac- 0.4453 g. (0.01388 atom) S, tural gradient furnace with tion pattern like that of 0.05 g. 11. 1,000 O. in hot zone and En GaiSi.

600 C. in cool zone. K Slo. rBae. GaInS; Pre-prepared SrGazS and The mixture was heated in a 10.550 6.322 10.658 711.9 Product gave a singlephase Balms. were ground together sealed evacuated silica tube EuGazSi-type X-ray difin a 1:1 mole ratio.- for 3 days at 1,000 0. fraction pattern, The calculated cell volume 01 71314.1 indicates nearly pertect solid solubility. L BaIn GaS 0.3763 g. (0. 222 mole) BaS, Sealed in evacuated quartz 10.65 6.424 10.861 743.4 Reddlsh-orange product gave 0.2551 g. (0.00222 atom) In, tube and heated in natural a single-phase EuGazSi- 0.1549 g. (0.00222 atom) Ga, gradient furnace for 2 days type X-ray difiraction 0.2137 g. (0.0067 atom) S, with hot zone at 960 C. and pattern. 0.05 g. 1;. cool zone at 400 0. Re-

ground and heated at 1,000 C. for 2 days.

PREFERRED EMBODIMENTS Examples 1 to 28, summarized in Table IH, are offered as illustrative of the invention and are not meant to limit the invention. Detailed Dcbye-Scherrer x-ray powder dif- TABLE III.-EXAMPLES 1-28 VII, and VHI, respec- Ex. No. Product Cell constants (A.) and cell volume (A?) Reactants Reaction conditions a b e V Remarks 1.... EuGaaSr 0.42 g. (0.0023 mole) EuS, Sealed in evacuated silica 10.233 6.108 10.354 646.5 Yellow product formed on 0.3182 g. (0.0046 atom) Ga, tube; heated for 48hours hot zone. Pseudo-ortho- 0.2236 g. (0.007 atom) S, in natural gradient iurrhombic crystal symmetry 0.05 g. I nace with hot zone at Eluoresced in both and 850 C. and cool zone at in daylight with emission- 300 0. (peak at 5430A. SemiconllOtOl with pn lK =2X10 ohm cm. 2.... YbGazSa 0.3524 g. (0.002 atom) Yb, Sealed in evacuated silica 10.041 6.066 10.056 612.5 Brown-red product in hot 0.284 g. (0.004 atom) Ga, tube; heated 3 days in zone. Structure pseudo- .2612 g. (0.008 atom) S, naturalgradientfurnace orthorhombic. 0.05 g. In. with hot zone at 800 C. and cool zone at 400 0.; reheated for 2 days with 1100" C. in hot zone and 800 C. in cool zone. 3.... YbGa SW 0.3189 g (0.00185 atom) Yb, Sealed in evacuated silica 10.485 6.338 10.501 697.7 Product which consisted of 0.257 g. (0.0037 atom) Ga, tube; heated 2 days in 7 red crystals plus a law .6821 g. (0.0074 atom) Se, natural gradient furnace white needles was washed 0.05 g I:- with hot zone at 950 C. with KOH solution and and cool zone at 600 0. water, leaving only red Reheated 2 days at crystals and trace of black 1,000 with no gradmaterial. Red crystals were lent. semiconducting YbGazSer 1157111110 gm" K,=4X105 and a ev. 4...- EuImS; 0.1842 g. (0. 1 mole) EuS, Sealed in evacuated silica 10.490 6.497 10.360 706.07 Product which was mostly 0.230 g. (0.002 atom 11, tube and heated 2 days yellow in color fluoresced 0.0963 g. (0003 atom) S, in natural gradient furdull red only at liquid 0.05 g. 1;. uses with 750 C. in hot nitrogen temperature. It zone and 300 C. in cool was a semiconductor with zone. Reheated 4 days m" ,=3X10 ohm-cm. with 1000 C. in hot zone and 600 C. in cool zone. 5.... EuGagSet EuSe/Ga/Se in 1/2/3 molar Sealed in silica tube pro- 10.666 6.3754 10.7945 734.0 Yellow-orange EuGarsea 6.... EuAhS;

7.-.. EIIGEISB 8---. YbAlaS 9...- EuImSer 10... EuAlzSea ratio; 0.05 g. Ia. tected by a thin layer of carbon on the inside degosited by pyrolyzing enzene therein at 900 0. Natural gradient furnace for 2 days with 800 C. in hot zone and 600 C. in cool zone.

0.4876 1;. (0.00265 mole) EuS, Heated in an A110; cruci- 10. 193 6. 060 10. 374 640. 8

0.1430 g. (0.0053 atom) Al, ble within an evacuated 0.2549 g. (0.0079 atom) S, silica tube for 2 days at 0.05 g. In. 800 C. (no gradient). Reheated at 1,000 C.

for 2 days.

EuSe/Ga/Se in 1/2/3 molar Heated in sealed evacratio; 0.05 g. I uated silica tube for 3 days in natural gradient furnace with 1,000 O. in hot zone and 800 C. in cool zone.

0 9742 g (0.0056 atom) Yb, Heated in sealed evacu- 0.3038 g. (0.0112 atom) Al, ated silica tube in na- 0.7221 g. (0.0225 atom) S, tural gradient furnace 0.05 g. I for 3 days with 875 C.

in hot zone and 300 C. in cool zone. 0.6622 g. (0.0 86 mole) EuSe, Heated in sealed evacu- 11.104 6.704 10.879 809.9

0.6585 g. (0.00574 atom) In, ated silica tube in na- 0.6793 g. (0.0086 atom) Se, tural gradient furnace 0.05 g. I for 3 days with 975 C.

in hot zone and 800 C. in cool zone.

0.8852 g. (0.00383 mole) EuSe, Heated in sealed evacu- 0.2096 g. (0.00777 atom) Al, ated silica tube in na- 0.9080 g. (0.0115 atom) Se, tural gradient furnace 0.05 g. I for 3 days with 950 0. in hot zone and 700 C. in cool zone.

0.0712 g. (0.00178 atom) Ca, Heated in evacuated 10.526 6 339 10.548 703.8

0.0456 g. (0.000198 mole) sealed silica tube in na- EuSe, 0.2753 g. (0 tural gradient tube furnace for 2 days with 1,000 C. in hot zone and 700 C. in cool zone. Reheated for 3 days with hot zone at 1,000 O. and cool zone at 800 C.

.00395 atom) Ga, 0.6079 g. (0.0077 atom) Se.

See footnotes at end of table.

formed in the hot zone. It was fluorescent with a peak at 528 millimicrons.

Large yellow flakes and yellow microcrystals oi EuAhSr. Anal. Cal'cd. Ior EllAlzSr: Eu, 45.47; Al, 16.15; S, 38.38. Found: Eu, 45.69; Al, 15.80; S, 35.9.

Mixture partly melted during reaction. Washed with dilute KOH. Composition verified by X-ray diffraction, density (calc. for 4 EuGaaSer/cell, 5.49 g.lcm. found 5.42 g./cm. and analysis. Cale: Eu 25. Ga, 22.96; Se, 52.01. Found:

E Ga. 22.63; Se

Most of the yellow product formed in hot zone, X-ray difiraction powder pattern like that of YbGazSr but with some additional Product was washed with cone. KOH. It consisted of bright gold-yellow crystals. Cell volume cal ed. for Can-"Enou- GazSe is 704.3 A. indicating that the formula is indeed very close to that represented. Product was highly fluorescent.

TABLE III-C0ntinued Cell constants (A.) and E cell volume (A!) No. Product Reactants Reaction conditions a b e V Remarks 12-.. SroaEuuGaInSfie; Pro-prepared SrGmSl and The mixture was heated 10. 628 6. 427 10. 008 724. 6 Product was a sintered, dark EuImSer were ground in a sealed evacuated honey-colored material together in a 1:1 mole ratio. silica tube ior 2 days at which gave the X-ray 1,000 C. diflraction pattern only of EuGazSrtype. The calcd. cell volume oi 731 A. indicates almost perfect solid solubility of the starting reactants.

13... Yba-rEuwGazSi Pre-prepared YbGazS. and .-...do 10. 134 6.075 10.374 638.7 The brick-red product gave E11G8z$4 were ground toa sin leEu GazSrtype X- gather in a 1:1 mole ratio. ray ction pattern.

The calcd. cell volume (629 As) is very close to that predicted and indiextensive solid solu- 14. Sr'o.rYbo.|GazS4 Pre-prepared SrGazS; and ..-do 10. 172 6. 087 10.238 633.9 The brick-red product gave YbG8zS4 were ground to a single EuGazSr-type X- gether in a 1:1 mole ratio. ray difiraction pattern. The calcd. cell volume of 633 A indicates nearly perfect solid solubility.

15... SruEuMGaInSm Preprepered SrGmSe. and ..-..do 10.846 6.569 10.864 774. 0 Product gave a single Euln se were ground EuGazs -type X-ray diltogether in a 1:1 mole ratio. traction pattern. The

cal cd. cell volume of 776 A. indicates nearly perfect solid solubility.

16... sra-rEuuGazszsem Pre-prepared EuGazSeaS and The mixture was heated 10. 388 6. 189 10. 534 677 Product gave a single-phase SrGazS4 were ground in a sealed evacuated EuGazSr-type X-ray diitogether in a 1:1 mole ratio. silica tube ior 12 hours traction pattern. The

, at 900 C. cal ed. cell volume oi 678 A. indicates nearly I perfect solid solubility.

17... SrmEunnImSl Sr/EuS/Inl3 in 0. 9/0. 1/2/ Sealed in evacuated '10. 541 6.497 10. 541 713. 7 Homogeneous orange cry- 3.9 molar ratio; 0. 05 g. I. silica tube and heated stalline product which in natural gradient gives a EuGarSr-type X- iurnace for 2 days ray diflraction pattern. with hot zone at 960 0. Anal. Cal'cd. for and cool zone at 600 C. SrMEuMImSu Sr, 17.44;

Eu,3.36; In, 50.81; S, 28.38. Found: Sr, 18.01; e u aos; In, 49.54; S,

18-- EuGaInSi 0.5521 g (0.003 mole) EuS, Sealed in evaucated 10. 251 6.307 10. 343 668. 6 Yellow-gold microcrystalline 0.2092 g. (0.003 atom) Ga, silica tube and heated product. The cal'cd. cell 0.344 g (0.003 atom 2 days at 1000" 0. volume of 676 A. indicates 0.2886 g. (0.009 atom) S, Reground and again that extensive solid 0.05 g. 1,. hoisted at l,000 C. for solution was achieved.

eye.

19- Sr ..Eu .-,Al S Br/EuS/Al/S in 0.9/0.1/ Placed in A110; crucible Product consisted oi mixture 213.9 molar ratio; 0.05 g. 1;. within evacuated sealed of red and green solids.

silica tube and heated The red solid had a reel:

3 days at 980 C. with salt-type structure. The

no temperature geen solid gave a gradient uGazSr-type X-ray diiiraction pattern and exhibited strong green iigiggeggencewith a peak a 20... Sr..-,Eu Ga=S Sr/EuS/Ga/S in 0.9/0.1] Placed in A110: crucible The mixture melted during 2/3.9 molar ratio; 0.05 g. 1,. in evacuated, sealed reaction. The plate-like silica tube and heated crystalline product ex- 4 days at 1050 C. hiblted strong yellow- Reground and heated green fluorescence. Its X- at 1000-1300" C. ior ray difiraction pattern about 2 days. showed it to be a EuGazSrtype phase.

21. Cao. rEu .uGa|S CaSlEuSlGa/S in Sealed in evacuated The yellow-cream-colored 0.95/0.05/2/3 molar ratio; silica tube and heated product exhibited strong 0.05 g. h. 2 days at 1000" 0. yellow fluorescence and a Reground at 1000C Eu GazS type X-ray and heated for 1 day. difiraction pattern.

22 EuGmSegB 0.378 g. (0.00205 mole) EuS, Heated in evacuated 10. 512 6. 291 10. 658 704.9 0range-brown product 0.2865 g. (0.0041 atom) Ga, sealed silica tube in formed in hot zone gave 0.4867 (0.00616 atom) Se, natural gradient tube gave a EuGarS4-type 0.05 g. I iurnace for 3 days with pattern and by Vegards 850 C. in hot and and aw had a formula of 370 C. in cold end. EuGmSeMSM. Semiconconductor with pas-V 7.4X10 ohm-cm- Thermal emi.=+1,600 v. per degree. Fluorescent when activated by UN.

23..- BM EU GMSGA 24... Ste-meEuo-eoozGazSt 0.5805 g. (0.004226 atom) Ba,

Placedin dried graphite 10.605 6.405

radiation. 11.17 758.7 Product solidified from the 0.244 g. (0.001057 mole) crucible which was melt as a yellow, poly- EuS, 0.7367 g. (0.01057 sealed in evacuated crystalline sohd which atom) Ca, 1.5853 g. silica tube and heated fluoresced yellow when (0.020077 atom) Se, 0.05 g. at 1050 C. for about 48 exposed to UN. radiah. hours. tion. The material gave an EuGazSrtype Debye- Scherrer pattern.

0.2787 g. (0. 18 atom) Sr, Sealed in evacuated silica Light yellow product gave 0 0001 (5.43Xl0' mole) tube heated slowly to a SrGazsi-type X-ray ditg. EuS, 0.4435 g. (0.00636 atom) 1,000 O. and held at traction pattern and fluo- Ga, 0.4080 g. (0.01272 atom) 1,000 C. for about 48 resced brightly, emitting S, 0.05 g. 1;. hours. yellow-green light. 0.644 g. Sr Gags. 1 0.0064 g. of pro- Reactants were ground to- The product had a pink color duct of Example N o. 24. gether and heated ior 2 typical of undoped SX'G84S| days at 900 C. in a sealed and fluoresced only weakly. and evacuated silica Spectographic examination tube. showed the presence oi See footnotes at end of table.

about 2 p.p.m. of Eu.

in en fluoresced 8) product gave a X-ray D 2. P (so at 1125 C. but when coole ,esced prodpowder attern and greenish flu d to (eale.)

Cell constants (A.) and cell volume (A!) V Remarks The white product i'luor moderately brightlyin U.V. light. Thus, ExamplesNo. 24, 25, and 26 show bri fluorescence for (St, @884 containing 0.02 atom gercent Eu, moderately right fluorescence at 0.002 atom percent Eu, and weak fluorescence at 0.0002 atom percent Eu. Pinlr microcrystalline not gave a Ca GaS4-typ ray powder diflraotion tern. It did not fluores' quid nitrog brightly (yellow-orang when exposed to U.V ation. Pink'lsh-white Sr Gazsr-type diflraction weak orescence at room temperature. in U.V. At liquid nitrogen temperature i! i'luoresced strongly in the yelloworange when expose U.V. radiation.

TABLE V-Continued d(nbs.)

TABLE III-Continued alumina crucible which was heated in a sealed evacuated tube for 3 days at 900 0.

Reaction conditions Reactants were put in an diam.)

Reactants in 10/1 molar ratio.

. (0.0032 atom) Ca,

. (5.8X10- atom) Yb, (0.0064 atom) Ga (0.0128 atom) .0015 atom 1 See preparation E. 2 See preparation A.

TABLE IV Powder pattern 0! Eu Ga s. produced in Example 1 No. Product 6-" S '0-mna 11o-onouzGazS4 SrGaz 4ISLoms IIo-MMGMSA 27... GammYbo-unozGazSa 28... SrmnuYbmoouGazSt TABLE V1 Powder pattern oi EuImS; produced in Example 4 NorE.--d=interplanar spacing in A.; I=relative intensity; q=1.ld.'.

ialer) (eale- NorE.-I=relative intensity; d=interplanar spacing in A.

TABLE V Powder pattern oi Yb Q8254 produced in Example 2 9730. 21 women mmm mmwnmmm 10665$985$5322099 5&AA&&32 ZZ Z2 ZZ2 KLL TABLE VIConti-uued I h k 1 (1(obs.) (c1110.)

NorE.--d=interplanar spacing in A.; I=relative intensity; q=l./d.

TABLE VII Powder pattern of EuGmSe. produced in Example 5 I h k 1 (obs-) (enlu Reflections not used- I dab. qi bs N oTE.-d=lnterp1anar spacing in A.; I=relative intensity; q=l./d.

TABLE VIII Powder pattern 01 ELlAlzS4 produced in Example 6 I h k I (obs) (culo I 0:11) qtobm N0'1E.d=interplanar spacing in A.; I=relative intensity; q=1./d.

UTILITY Semiconductivity As shown in Table III, the resistivity of the products of this invention is between 10 to 10 ohm-cm., that is, in a range intermediate between that of good conductors, 10- ohm-cm., and that of insulators, 10 to 10 ohmcm. The products show a negative change of resistivity with increase in temperature and are useful components in semiconductor devices such as rectifiers, modulators, detectors, thermistors, photocells, and crystal triodes or transistors.

The temperature dependence of resistivity maybe illustrated by that of YbGa Se produced as described in Example 4. Resistivity at 298 K was 4x10 ohm-cm. as contrasted to 3x10 ohm-cm. at 370 K. The activation energy, E,,, was 0.3 ev. Ytterbium digallium tetraselenide and the various products of the inventino may be used to determine temperature by pre-establishing the relationship of log of resistivity of the material to the reciprocal of absolute temperature and then simply measuring the resistivity of the material and reading its temperature from the temperature-resistivity plot.

EXAMPLE A Use as a rectifier and as a photovoltaic generator This example illustrates the use of the novel compositions as semiconductors. Specifically, this example describes the use of a crystal of europium diindium tetraselenide, EuIn Se in rectification of electricity and in a photovoltaic cell to convert visible light directly into electricity.

A crystal of EuIn Se of flake-like crystal habit and a small piece of gallium were heated in a sealed evacuated silica tube at about 600 C. for 12 hours and then quenched. This vapor phase doping resulted in a superficial coating of the EuIn Se with gallium. Whereas the crystal had originally been fluorescent only at very low temperature, it now was fluorescent in visible light at room temperature.

The surface-doped crystal 'was mounted in rubber cement, leaving only one surface exposed, and the exposed surface was then etched to remove the gallium-containining layer by brief treatment in concentrated hydrochloric acid. The surrounding rubber cement was then removed from the other surfaces. The etched face was no longer fluorescent, although the other faces retained their fluorescence. Electrical contacts were attached to the etched and unetched surfaces using silver paste, and resistance 19 of the crystal was measured by means of a Senior Volt Ohmyst. The crystal acted as a rectifier, for when the Ga-doped side was negative, the resistance was 200x10 ohm, and when the electrodes were reversed, the resistance was 500x10 ohm.

The etched crystal was also strongly photoconducting. A photovoltage was generated simply by shining light from a microscope lamp directly onto the crystal. The generated voltage was measured by a Senior Volt- Ohmyst and found to be about 0.4 volt maximum with actual voltage dependent upon the intensity of the light beam.

Luminescence The novel compositions disclosed herein are, inter alia, luminophors or luminescent materials and, upon activation by means of appropriate radiation, e.g., ultraviolet or visible light, they luminesce emitting non-thermal radiation in the visible region. The color of luminescence can be controlled by varying the ionic character, i.e., the specific'metallic components, of the compositions.

Compositions of this invention exhibit very bright cathodoluminescence as well as photoluminescence. Cathodoluminescence is the luminescence resulting from excitation of a phosphor (fluorophor) by means of cathode rays (beta rays). The property of cathodoluminescence makes the compositions useful in color television and in oscilloscopes.

visible light that ranges in color from bluish-green to yellow:

Wavelength in A.

Exciting Emission Composition radiation pea Inasmuch as 4000 A. radiation is part of the visible spectrum, it is apparent that the europium-containing compositions may be activated by visible light and more especially by sunlight which has a wave length extending into the UV region. Tests have shown that visible light of 4600 A. is even more eflicient than UV light in exciting Euga S Europium-containing compositions with high indium content must usually be cooled below room temperature before fluorescence is observed. The luminescence of Z Eu (Al,Ga) X compositions changes from yellow to blue-green as the ionic character of the metallic components increases, i.e., compositions containing calcium and gallium tend to emit in the yellow whereas compositions containing strontium and aluminum tend to emit in the blue-green.

Ytterbium-containing compositions of the invention usually fluoresce with a yellow-orange color. It is fre- 20 v m quently necessary to cool the compositions below room temperature to induce strong fluorescence.

F. A. Kroger reports in Some Aspects of the Luminescence of Solids, Elsevier Publishing Company, Inc., Netherlands, 1948, p. 237 that As a rule the efficiency of the luminescence as a function of the activator concentration increases at low concentrations but decreases again at higher concentrations, giving a maximum luminescence in an intermediate concentration region. In partial agreement, the luminescence of the products of this invention usually decreases as the y of general formula i-y yoz is decreased below 0.01. However, there appears to be little or no decrease in luminescence as y is increased above 0.01 and, in fact, luminescence is observed with y equal to 1 in the compositions EuGa S EuGa Se EuAl S and, when cooled, in EuIn S Eu'In Se YbGa -S and YbA S Fluorescence is also observed with and oss uos z z z- Luminescence activated by daylight and visible in daylight is fairly common among organic phosphors but is rate among inorganic substances. It is particularly desirable in inorganic luminophors since they should be more efiiicient, versatile, and durable than organic phosphors.

The luminophors of this invention are useful as luminescent components in various materials and articles such as plastics, displays and paints, as light sources, in a mixture with other phosphors to obtain additive colors, and in general for many of the well-known applications of luminophors.

EXAMPLE B Use of products of the invention as a source of light was demonstrated by placing vials of EuGa S Ca Eu Ga S Ca Eu Ga S and EuAl S in turn in a. dark box fitted with an ultraviolet lamp. Paper on which a statement had been written was also placed in the dark box. A window at the top permitted inspection of the interior of the box. When the UV lamp was turned on, each of the Eu-containing compositions glowed with such brightness that the viewer was able to read the statement on the paper. Without the luminophors, light from the UV lamp was not sufiicient to permit the statement to be read.

EXAMPLE C This example illustrates the use of the daylight fluorescence of EuGa S to increase the visibility'of a typical plastic. A small amount of EuGa S was dispersed in styrene monomer and methyl ethyl ketone peroxide catalyst was added to induce polymerization. The resulting polymer fluoresced with a bright yellow color in day- This example shows the efliect of substituting small quantities or dopants into typical products of the invention. The dopants in elemental form were included in typical reaction mixtures which were heated in sealed evacuated tubes in the manner described in Table 1H. The exact extent of doping is difiicult to determine and is not reported, but the shifts in reported fluorescence, in cell dimensions, and/or in resistivity at 298 K. show that the dopant was actually incorporated:

Element Doping partially Final element replaced composition Properties of product None- None.- EuGa si Bright yellow fluorescence;

p=2 X10; ohm-cm. Er (Eu, Yb)- Er-doped (Eu, Yellow-orange fluorescence.

Yb) Q8284. Te Se. Te-doped Orange fluorescence; cell EuGarSen dimensions shifted to slightly larger cell. Cu Eu Cu-doped Yellow fluorescence weaker EllGazsl. than that of EuGazsa; =l.1 X10 ohm-cm. Cr Ga Cr-doped Feeble yellow fluorescence;

EuGazS4. p=l.0 X10 ohm-cm. Ag Eu rigs-doped Bright oran e fluorescence;

uGazSr p=7.7 X10 ohm-cm. Sm Eu Sm'doped Very weak orange fluores- EuGazSr cence; little shift in cell dimensions; p=1.1 X10 ohm-cm. Sm Eu Srn-dop d Small shift to larger cell EuIngSn dimensions; nonflcorescent at room temperature. Cu Ga Cu-doped Very little fluorescence.

Eu Gasi.

EXAMPLE E Doping of previously grown crystals does not necessarily give the same results as introduction of dopant during synthesis. The dopant may diffuse only part way into the crystal (usually with material lowering in resistivity). Unidentified surface species may be formed which may be responsible for the change in properties. In other cases the dopant may enter uniformly into the crystal lattice. Doping by vapor-phase treatment may, as described in Example A, result in materials useful as rectifiers and in photovoltaic cells. The results of doping typical products of the invention by heating them with various elements and immediately quenching are tabulated below. The positive values of thermoelectric power (microvolts per degree) show that the doped crystal are p-type semiconductors:

Properties of doped crystal Fluorescent coating.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 1. A semiconducting and luminescent composition characterizd by pseudoorthorhombic crystal structure and the formula Qa e wherein:

M is selected from at least one of En and Yb, Q is selected from at least one of Al, Ga and In, X is selected from at least one of S and Se, and with the proviso that when M consists of or includes Yb, then Q is selected from at least one of A1 and Ga. A composition according to claim 1 wherein M is A composition according to claim 1, EuGa S A composition according to claim 1, EuIn S A composition according to claim 1, EuGa Se A composition according to claim 1 EuA1 S A composition according to claim 1, EuIn Se A composition according to claim 1, EuAl Se A composition according to claim 1, EuGaInS 10. A composition according to claim 1, EuGa Se S. 11. A composition according to claim 1, wherein M is 12. A composition according to claim 1 wherein Q is selected from at least one of Al and Ga. 13. A composition according to claim 1,

References Cited UNITED STATES PATENTS 2,814,004 11/1957 Goodman 233 15 3,174,939 4/ 1965 Suchow 23315 3,639,254 2/ 1972 Peters 252301.45

OTHER REFERENCES Bull. Soc. Chim. Fr., (3), 747-50 (1971, March), disclosed in Chemical Abstracts vol. 75, 41422f.

Lotgering, J. Phys. Chem. Solids, vol. 29, p. 699 (1968).

Advanced Inorganic Chemistry, Cotton and Wilkinson, 23d ed.i John Wiley & Sons, Inc., New York (1966), pp.

OSCAR A. VERTIZ, Primary Examiner J. COOPER, Assistant Examiner US. Cl. X.R. 

